The media works hard on sensationalizing the pitfalls for students using the internet and naturally many parents shut down and keep their children offline or hesitate to authorize their children's participation.
When you started out with a classroom wiki/ning /blog/etc -
What did you say to the parents to get them on board?
What CMS did you use?
Was your wiki/blog public or private.
If it was private how did you set up a private conference so that parents could participate and students keep it private?